1. Field of the Invention
The present invention relates to an apparatus for stacking generally planar articles of material. More specifically, the present invention relates to an apparatus for stacking generally planar articles of material that includes at least one safety sensor and a safety controller for reducing the risk of injury to persons near the apparatus.
2. Description of the Related Art
Devices for stacking generally planar articles of material, such as sheets of corrugated material, are well known. One example of a commercially available device is the AGS2000 Rotary Die Cut Stacker made by the assignee of the present invention, A.G. Machine, Inc., Weyers Cave, Va. Further examples of such devices are disclosed in U.S. Pat. Nos. 3,321,202 to Geo. M. Martin and 3,419,266 to Geo. M. Martin, each of which is expressly incorporated herein by reference in its entirety.
FIGS. 1 and 2 illustrate a conventional apparatus for stacking corrugated blanks. The stacking machine 100 generally comprises a layboy section 102 which receives conjugated blanks, such as those produced by a rotary die cut machine (not illustrated), and discharges the corrugated blanks onto a transfer conveyor 104. The transfer conveyor 104 receives the blanks and transports them to a main conveyor 106. The main conveyor 106 has an intake end 108 and a discharge end 110. At intake end 108, the main conveyor 106 is mounted to a base 112 at a pivot point 114 so that the conveyor may be pivoted to raise the discharge end 110 of the conveyor 106. At the discharge end 110 of the conveyor 106, an accumulator section 116 receives discharged blanks.
In operation, the main conveyor 106 is pivoted about the pivot points to lower the discharge end 110 of the conveyor to an initial position. Sheets are fed onto the main conveyor 106 at its intake end 108, transported along the distance of the conveyor to its discharge end 110, and discharged from the conveyor over an accumulator faceplate 121 having a lower end 123. The sheets are discharged and often strike a backstop 118, having a lower end 119, in the accumulator section 116 which stops the forward momentum of the sheets. The stopped sheets settle down, typically onto a discharge conveyor 132, to form a stack of sheets. As additional sheets are placed on the stack, the main conveyor 106 is pivoted to raise the discharge end 110 vertically so that the discharged sheets are discharged above the top of the growing stack.
Once a stack of sheets is completed, it must be removed to allow additional stacks of articles to be formed on the discharge conveyor. To allow the stack to be removed without stopping the main conveyor 106, catcher elements 120 in accumulator section 116 are extended beyond and below the discharge end 110 of the main conveyor 106 so that sheets leaving the discharge end 110 of the main conveyor 106 fall onto the catcher elements 120. A small pile of sheets is formed on the catcher elements 120 while the stack on the discharge conveyor 132 is removed, and when the stack is clear of the accumulator section 116, main conveyor 106 is lowered, and the catcher elements 120 are withdrawn to deposit the pile of sheets from the catcher elements 120 onto the discharge conveyor 132 to form the beginning of a new stack of sheets onto which additional sheets from the discharge end of the main conveyor 106 are deposited.
The main conveyor 106 is massive, moves relatively quickly from a raised to a lowered position, and can maim or kill a person who is present therebeneath when lowered. Of particular concern are the pinch point formed between the bottom 119 of the accumulator backstop 118 and the discharge conveyor 132 and the pinch point formed between the bottom 123 of the accumulator front plate 121 and the discharge conveyor 132. Either of the pinch points could crush an object, including a user or user's body part, that is in the pinch point when the main conveyor descends. A person standing beneath the main conveyor 106, upstream of the accumulator faceplate 121, for example, could also be severely injured when the main conveyor 106 descends.
Previous attempts to protect machine operators have often focused on perimeter protection, as disclosed, for example in U.S. Pat. No. 6,986,635 and U.S. Pat. No. 7,104,747, both issued to Talken et al. Such systems use a light curtain or one or more beams of light that are broken when a user approaches a dangerous area. However, when the light curtain is too close to an operating piece of machinery, it may not be possible to stop the machine in time to avoid user injury. When the light curtain is too far away from the operating machinery, however, it may frequently be tripped by accident and cause unnecessary shut downs of the machine being protected. Light curtains also do not address the scenario of a person being present between the light curtain and the area of danger when another operator resets the safety system leaving that person exposed to possible injury when the machine resumes operation.
It would therefore be beneficial to provide an article stacking apparatus that is configured to reduce or eliminate human injuries.